In recent years, a reduction in fuel consumption of a vehicle is required from the viewpoint of environmental protection. Along with this, a reduction in rolling resistance is required for a pneumatic tire.
A hysteresis loss that is a main cause of rolling resistance of a pneumatic tire increases in a tread portion to contact a road surface and adjacent portions. There is a known method of reducing a hysteresis loss caused by deformation of a tread portion, which makes a bead portion easy to deform by decreasing the stiffness in a tire radial direction (a stiffness in a radial direction) of a bead portion located in a lower part of a sidewall, disperses the deformation of a tread portion to a bead portion, and decreases a hysteresis loss caused by the deformation of a tread portion.
On the other hand, the stiffness of a part ranging from a bead portion to a side wall portion of a pneumatic tire contributes to a vehicle stability to rolling and pitch, and if the stiffness in a radial direction of a part ranging from a bead portion to a side wall portion is set extremely low, a driving stability may decrease.
To solve the above problem, the applicants have proposed a pneumatic tire that reduces a rolling resistance without extremely decreasing stiffness in a radial direction (see Patent Literature 1).
In a pneumatic tire of the Patent Literature 1, a stiffener is disposed more outside than a bead core in a tire radial direction, a most thickness portion of a rubber chafer is disposed outside a carcass turn-up portion in a tire width direction and in proximity of an outer end of a stiffener in a tire radial direction, a sectional area of a stiffener with respect to a sectional area of a rubber chafer is 0.5 or lower, and a rubber with JIS A hardness of 80 degrees or higher is disposed in an area between a carcass crown portion and a bead core.